This application addresses broad Challenge Area (12): Science, Technology, Engineering, and Mathematics Education (STEM), and specific Challenge Topic (12-OD-101*): Efficacy of Educational Approaches toward Promoting STEM Competencies. The proposed large-scale, randomized control trial will assess the efficacy of the Core Knowledge Preschool program in promoting the math and science skills of 3- to 5-year old children at risk for academic difficulties due to socioeconomic disadvantage. Specifically, this research will (1) determine the impact of the Core Knowledge Preschool program on the types and amounts of math and science instruction offered in preschool classrooms;(2) determine the impact of the Core Knowledge Preschool program on preschool children's math and science learning, engagement, and interest;and (3) investigate for whom and under what conditions the Core Knowledge Preschool program may yield positive results. The Core Knowledge Preschool program is a fully-developed, commercially-available, comprehensive preschool curriculum that emphasizes academic content (math, science) as well as oral language, literacy, and socio-emotional development. The math and science components of the program, of relevance to this proposal, provide full scopes and sequences for these domains, including specific skills to be taught and guidance on effective teaching practices and activities as aligned with current research and education standards. Participating preschool teachers and children enrolled in their classrooms will be randomly assigned to either implement the Core Knowledge Preschool program or to a business-as-usual control condition. Teachers assigned to the Core Knowledge Preschool condition will be provided with the Core Knowledge Preschool curriculum, supporting materials, and 72 hours of in-service professional development, and asked to implement the program in their classrooms for one full academic year. Teachers assigned to the control condition will receive equivalent amounts of classroom materials and professional development but continue providing their typical classroom instruction. Core Knowledge Preschool and control teachers will be compared on pre- and post-implementation classroom math and science instruction (quality, types, and amounts) using data coded from classroom observations. Children in Core Knowledge Preschool and control classrooms will be compared on gains (pretest, posttest, 6-month follow-up) on curriculum-based and psychometric measures of math and science knowledge and interest as well as objective indicators of children's engagement in math and science activities from classroom observations. Child characteristics (e.g., gender, age) and teacher characteristics (e.g., fidelity of implementation, years of experience) will be examined as potential moderators of effects to determine for whom and under what conditions the Core Knowledge Preschool program may be efficacious. Public Health Relevance: Science, technology, engineering, and math competence is increasingly important for personal and economic success in the 21st century, and lack of knowledge in these areas may have substantial academic, psychosocial, and economic consequences for individual and society at-large. Effective math and science preschool education holds great promise for not only ensuring success in these domains, but also reducing present disparities between children from advantaged and disadvantaged backgrounds, thus addressing important public health issues.